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Darwin Correspondence Project

From H. C. Sorby   3 January 1882

Broomfield | Sheffield

Jan 3/82.

My dear Darwin

I very much wish I could give a more satisfactory report but perhaps what I have been able to do may be of some use to you. Besides the cause you suggest the blue colour ⁠⟨⁠mi⁠⟩⁠ght have been due to two other causes.1 A colouring matter in a dilute acid state might have been already present in that peculiar molecular state into which so many pass when diluted, where they cease to have any colour. Of course I mean quite independent of mere weakening of the solution. If such were the case it might turn blue when the acid neutraliz⁠⟨⁠ed⁠⟩⁠ but at the same time would also turn red when such a strong acid as hydrochloric is added. This is not the case so I do not think any material amount of a coloured substance is present. In the second place a colouring matter might have been formed by oxidization when the acid neutralized, as I reasoned previously. And here I am bothered. When boiled with alcohol some thing is ⁠⟨⁠5 or 6 words⁠⟩⁠n water which appears to pass so rapidly into a brown substance with curious shade of green that the real change is quite hidden. There may be a red pigment also formed which would be changed to blue by an alkali but the deep brown colour disguises the effect too much to enable me to be certain

On the whole the facts differ a good deal from what I had observed with flowers &c but then I had made very few experiments with colourless stems.2 Before being able to give any more confident opinion I should have to work out the whole thing as an independent inquiry. Much as I should like to do this, I cannot well undertake it since I have already promised to do as much as I shall be able to finish before I leave home again. In any case however what I have done will as far as it goes remove some doubts and will make your supposition more probable. Until examined as I have done the question was as I have explained open to several different explanations.

Wishing you a happy new year and trusting that you will be able to throw further light on the interesting facts to which you have called my attention

I remain | Yours very truly | H. C. Sorby

CD annotations

1.8 I do not think … present. 1.9] scored red crayon
1.9 coloured … present.] underl red crayon
1.10 oxidization] ‘oxidization’ pencil
2.1 On the whole … flowers] scored red crayon

Footnotes

No letters from CD to Sorby on this subject have been found. In December 1881, Sorby had replied to a query from CD about colour changes in plants; he had described the changes arising from oxidisation, and from exposure to acidic and alkaline solutions (see Correspondence vol. 29, letter from H. C. Sorby, 28 December 1881).
Sorby had observed plant pigments using a modified microspectroscope that he first developed to examine mineral specimens. His research interests included the optical and chemical properties of chlorophyll, colour changes in autumn leaves, and comparisons between the colouring matter of plants and simple forms of animal life. See Sorby 1871 and Sorby 1873.

Bibliography

Sorby, Henry Clifton. 1871. On the various tints of autumnal foliage. Quarterly Journal of Science 8: 64–77.

Sorby, Henry Clifton. 1873. On comparative vegetable chromatology. Proceedings of the Royal Society of London 21 (1872–3): 442–83.

Summary

Reports the inconclusive results of some experiments he has been doing for CD [related to plant colouring material?].

Letter details

Letter no.
DCP-LETT-13598
From
Henry Clifton Sorby
To
Charles Robert Darwin
Sent from
Broomfield, Sheffield
Source of text
DAR 177: 220
Physical description
ALS 7pp damaged †

Please cite as

Darwin Correspondence Project, “Letter no. 13598,” accessed on 28 March 2024, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-13598.xml

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